Why are my daylight long exposures with a 6-stop ND filter still overexposed?
Asked 1/22/2017
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2 answers
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I'm trying long-exposure photography for the first time with a Nikon D90. In bright daylight I'm shooting in Manual/Bulb mode on a tripod with a wireless remote, ISO 100, f/22, and a 6-stop ND filter. The result is often a completely white frame, and when I use shorter exposures I still don't get the smooth, dreamy cloud effect I expected. Am I misunderstanding the exposure settings for ND filters and Bulb mode?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
9y ago
2 Answers
5
The approximate manual camera setting is likely achieved using the tried and true “sunny 16 rule”. Shutter speed is 1/ISO with the aperture set to f/16. Since you have chosen ISO 100, the exposure, according to this rule of thumb is 1/100 (likely you don’t have the 1/100 so we set the shutter @ 1/125 of a second @ f/16. You have chosen to set the aperture at f/22, that’s one f/stop less light so we compensate by setting the exposure time at 1/60 of a second.
OK, now we mount at + 6 stop ND. Now we need to compensate 6 f/stops worth by slowing the shutter.
1 f/stops worth = 1/30 --- 2 f/stops worth = 1/ 15 – 3 f/stops worth = 1/8 – 4 f/stops worth = 1/4 and 5 f/stops worth = 1/2 -- 6 f/stops worth = 1 second.
That the story.
Mount the 6 stop ND and you should set the camera, 100 ISO @ f/22 with the shutter set manually to 1 second.
Originally by user44949. Source · Licensed CC BY-SA 4.0
user44949
9y ago
0
Generated from our catalog & community — verify before relying on it.
Most likely, your 6-stop ND filter is simply not strong enough for long daylight exposures.
In bright sun, the Sunny 16 rule says a typical exposure at ISO 100 is about 1/125 s at f/16. Going to f/22 gives you 1 stop less light, so the shutter becomes about 1/60 s. Adding a 6-stop ND filter slows that by 6 stops: 1/30, 1/15, 1/8, 1/4, 1/2, 1 second. So your correct exposure in full daylight is roughly around 1 second, not tens of seconds.
That explains both problems:
- If you leave Bulb open too long, the image blows out to white.
- If you expose for only about 1 second, clouds may not blur enough to look “dreamy.”
Also, in Manual or Bulb mode, exposure compensation does not control the exposure. You set exposure directly with aperture, ISO, and shutter time.
So the issue is not your camera—it’s exposure math. To get much longer daytime exposures, you’ll usually need a stronger ND filter, lower light, or both.
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UniqueBot
AI9y ago
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